There has long been a need, particularly in industrial and commercial facilities, for a device which functions to turn on and off one or more electrical load circuits at the facility at preselected times so as to conform the "on time" of the load circuit with the periods during which energization of the loads associated therewith is required. For example, it may be desired to turn on the air conditioning equipment at the facility about an hour before the beginning of the normal working day, and to turn off the air conditioning equipment about an hour after the end of the normal working day. As another example, it may be desired to limit energy consumption at the facility by turning off certain load circuits during times that energization of the loads associated therewith is not essential.
In the prior art, this need has been met for the most part by electro-mechanical timers which include an electrical clock, typically powered from a source of alternating current voltage, and a plurality of manually positionable switches which are assembled so as to be actuated by a cam, rotated by the clock, whose position represents real-time. Such timers usually are adapted only for the control of a single load circuit, and are capable of providing only a limited number of changes in the energization states of the load circuit during a single 24-hour period. The switches are difficult to position, and their physical construction does not permit a precise selection of on-off times. Further, the control function afforded by such timers is simply to turn the load circuit on or off, and more sophisticated control functions, such as duty-cycle control of the load circuit, are not available. Finally, a power outage which causes a disruption in the source of alternating current voltage causes the timer to lose synchronism with real time, so that the position of the cam therein must be manually readjustable after restoration of power.
Another type of device typically used in the prior art is that known as the repetitive cycle controller, which functions to provide control of the energization states of one or more load circuits in accordance with a predetermined duty cycle, that is, each load circuit is repetitively turned on and off for predetermined periods of time. Such repetitive cycle controllers, however, are difficult to use to effect control of the energization states of a load circuit in accordance with a predetermined time schedule.
It is therefore an object of this invention to provide an improved apparatus for controlling the energization states of a plurality of electrical load circuits in accordance with a predetermined time schedule.
It is a further object of this invention to provide such an apparatus which takes the form of a programmable electronic real-time load controller which is operable to control the energization states of the load circuits in real time and in accordance with a predetermined time schedule that has been programmed into the controller by a user.
It is another object of this invention to provide such an apparatus which allows a user to flexibly program the predetermined time schedule by selecting, in advance, a number of control events and corresponding event times for each of a plurality of load circuits and for each of a plurality of days in a week.
It is yet another object of this invention to provide such an apparatus which allows the user to select a control event which causes a particular load circuit to be turned on, to be turned off, or to be controlled in accordance with a predetermined duty-cycle control function.
It is still another object of this invention to provide such an apparatus which allows the user to select, in advance, a holiday schedule for each load circuit, and to designate in advance a particular day of a week as a holiday, whereupon the apparatus functions to control the energization states of the load circuits during the designated day in real-time in accordance with the holiday schedule.
It is an object of this invention to provide such an apparatus which permits the predetermined time schedule to be overridden by an external device, or, by the user.
It is an object of this invention to provide such an apparatus in which the operation of the apparatus is maintained in synchronism with real-time despite the loss of ac power to the apparatus.
It is an object of this invention to provide such an apparatus which can be implemented in an easy and inexpensive manner by the use of readily available, integrated circuit, microprocessor components.